Dielectric materials are used in a wide variety of electronic circuit applications. In semiconductor applications these of materials often consist of silicon chemically combined with oxygen or nitrogen. Such dielectric materials are used as capacitor elements, gate insulators for field effect transistors and insulators in metallization systems. Silicon oxides are among the most common of dielectric materials used in semiconductor manufacture, but as device geometries continue to shrink the performance requirements of component materials is increasing beyond that which is attainable with silicon oxide. Accordingly, alternate dielectric materials are sought.
In certain applications, such as interlevel dielectrics for multilevel metallization systems, it is desirable for the insulator material to have a low dielectric constant relative to silicon dioxide. These insulators are generally referred to as low k dielectric materials. In contrast, to provide increased charge storage in capacitor elements, and lower switching voltages in Metal Oxide Semiconductor (MOS) Field Effect Transistors (FETs), it is desirable that insulator materials for these applications have high dielectric constants relative to silicon dioxide. Insulators in this class are generally referred to as high k dielectric materials.
Process integration and performance issues have severely limited the application of available high k materials in lieu of silicon oxides. This is particularly true for provision of FET gate insulators. That is, although insulators such as tantalum pentoxide and titanium dioxide have relatively high dielectric constants, these and other materials are not thermally stable when in direct contact with silicon.
Recently, evaluations have been performed on various high k silicate dielectrics to assess their performance and suitability for integration with semiconductor manufacturing processes. See, for example, Wilk, et al., “Electrical Properties of Hafnium Silicate Gate Dielectric Deposited Directly on Silicon,” Applied Physics Letters, Vol. 74, No. 19, May 10, 1999. Problems with interface states and leakage currents have so far precluded application of these materials to gate and capacitor dielectrics in volume manufacture of semiconductor products. Generally, with continued increases in the density of semiconductor circuitry, there is a need for high k dielectric materials which provide satisfactory electrical and physical properties in order to provide higher performing gate and capacitor insulators in ultra large-scale integration (ULSI) applications.